1. Field of the Invention
The present invention generally relates to a projector apparatus. More particularly, the present invention relates to a contrast adjustable projector apparatus having a nontelecentric architecture.
2. Description of Related Art
The projector has become a commonly used image device in the office, the meeting room or at home. The projector includes the liquid crystal on silicon (LCOS) projector and the digital light processing (DLP) projector. There are two types of the DLP projector, including the telecentric architecture and the nontelecentric architecture. Compared with the LCOS projector, the image performance of the DLP projector is better, therefore, the DLP projector has become the mainstream in the market.
Because the DLP projector has a built-in digital micromirror device (DMD) which provides better image projection quality, therefore, the DLP projector has a superior performance. FIG. 1 is a schematic diagram showing the relationship between the rotation of the DMD (actually, the DMD is the digital micromirror unit 10) and each optical element. The projector mainly comprises a light source 14, a lens 16, a DMD 10 and an integrator 18. Each digital micromirror unit 10 is corresponding to each pixel of the projector 200. After the light source 14 emits a light, if the digital micromirror unit 10 receives an on-state signal, it would rotate to a tilt angle (+θ) as the digital micromirror unit 10a. Thus, the light travels through the lens 16 and the corresponding pixel performs an on-state. If the digital micromirror unit 10 receives an off-state signal, it would rotate to a tilt angle (−θ) as the digital micromirror unit 10b. At this time, the light is incident to the integrator 18 and the corresponding pixel performs an off-state. Generally speaking, θ is about 10 degree to 12 degree. However, if the digital micromirror unit 10 does not rotate or rotates to 0 degree, the corresponding pixel performs a flat state; Because the flat state is an unsteady state, therefore, the scattering light would be incident to the projector and the contrast of the whole screen would be lower.
The brightness of the projector is in conflict with the contrast substantially. It means that if the image brightness is higher, the contrast would be lower. On the contrary, if the image brightness is lower, the contrast would be higher. Because the conventional DLP projector can only provide constant contrast and brightness, therefore, the flexibility of the applications of the DLP projector is not sufficient. The capability and the value of the DLP projector are lower.
In U.S. Patent Publication No. 2005/0036216A1, an image display apparatus having a telecentric architecture is disclosed. A tunable illumination mask having an illumination hole is positioned at the location of an illumination stop. The tunable illumination mask comprises a plurality of movable diaphragms which overlap with one another to form the illumination hole. The size of the illumination hole is adjusted by adjusting the movable diagrams to effectively block light of noise-type. However, the requirements for setting the tunable illumination mask are very restricted, such as the position, the mechanical design, etc. Besides, the tunable illumination mask blocks light of noise-type in each area and light in an on-state would also be blocked, too. Although the contrast of the image display apparatus can be enhanced, the brightness is drastically decreased. The display quality is lower. In addition, it's harder to set up the tunable illumination mask in lenses and the requirement for precision is higher. Therefore, the cost of the lens and the whole image display apparatus is higher, and product is less competitive on the market.
In light of the above, the solution of how to enhance the contrast with the limited reduction of the brightness under the condition of simple fabrication process and lower cost is highly desired in the technology of the projector industry.